The "good old latency" issue. I have a recording studio (using Sonar software) and those of us that have computer based studios latency is a prime issue for our equipment.
Have you run the DPC Latency Checker Download HERE
ASIO was mentioned, The Xfi sound card that I used to have did have ASIO (the reason I uninstalled it - the Creative ASIO was interferring with my studio ASIO hardware).
The CMOS (BIOS) backup battery failure would cause the BIOS to revert to default settings but shouldn't have caused any other problems. Are you sure you have the BIOS settings back to how you originally had them? Not sure what could cause the problem, that you didn't have, unless possibly overclocking????
One other thought, are you actually using the Line In or are you using the What You Hear as the default playback device? I recall someone on the Dell forum was having latency problems with the PC audio and they changed the default playback device from the System Mixer (SoundBlaster calls this What You Hear) to the mic (they were using the mic input) and it got rid (minimized) of their latency problem.